Producing sets of digital pulses having a desired skew, or delay, between pulses is useful in a variety of applications, including telecommunications, radar, high speed sampling systems and time measurement systems. To be useful for these applications, the skew between the pulses in the set should be known by the system to a high degree of precision. Time measurement systems used for characterizing the timing of the propagation of electromagnetic radiation, such as human-visible light or radio waves through a medium must be exceptionally precise. As an example, an uncertainty of one nanosecond in timing the distance that a radio wave has traveled will result in an uncertainty of 0.3 meters. Accordingly, precision timing circuits have been designed to provide pulse sets with a high degree of precision.
By way of illustration, FIG. 8 depicts an example of a system 1 corresponding to an existing approach that can be utilized to produce a set of pulses PULSE1 AND PULSE2. The system 1 includes a high speed clock 2 and one or more programmable counters 3 and 4 to produce a set of skewed pulses PULSE1 AND PULSE2 for precision timing applications. The counters 3 and 4 are enabled by respective input pulses and are driven by the high speed clock 2. In the system 1, the counter 3 is enabled by an INPUT signal and the counter 4 is enabled by the output of the other counter 3 (PULSE1). Each counter 3, 4 can be programmed to trigger an output pulse PULSE1 AND PULSE2 after a desired number of clock cycles (e.g., based on PROG1 and PROG2, respectively). In a simple radar, time measurement or range finding application, a first pulse can be provided on a first path at a desired interval. For example, the clock 2 can drive the counter 3 having a programmed value representing a desired pulse repetition rate (PRR) for the system 1. Each time the first counter 3 emits PULSE1, the first counter 3 is reset, such that another pulse can be provided at the desired PRR. The second counter 4 can be enabled by the PULSE1 to produce PULSE2 on a second path, with its programmed value representing a desired skew value for the system 1. By controlling the programmed values (PROG1 and PROG2) at the counters 3 and 4, the PRR and the skew of the signal can be varied.
A disadvantage of the above and other existing approaches is the inability to provide pulse repeat intervals greater than the skew between the two paths. For example, in the counter-based implementation described above, both counters must be reset with each pulse from the first counter. Accordingly, if the delay at the receiver path counter is greater than the delay at the transmitter path counter, the receiver path counter will not be able to finish counting down before it is reset by a next transmitter pulse. This limits the range and accuracy of systems utilizing this form of timing as well as the potentially useful applications for such an approach.